In general, when a compound is used as an effective active ingredient of a pharmaceutical, the chemical and physical stability of the compound is required in order to keep the quality stable and/or facilitate the storage management. Therefore, the obtained compound is preferably in a stable crystal form and in general the most stable crystal form is often selected as a drug substance for a pharmaceutical.
So far, a plurality of HSP90 inhibitors have been reported as an antitumor agent, for example, Patent Document 1 and 2 describe 3-ethyl-4-{3-isopropyl-4-(4-(1-methyl-1H-pyrazol-4-yl)-1H-imidazol-1-yl)-1H-pyrazolo[3,4-b]pyridin-1-yl}benzamide (hereinafter also referred to as “Compound 1”) as a compound which has excellent HSP90 inhibitory action and shows antitumor activity.
Meanwhile, although a pharmaceutical composition for oral administration requires in general not only the stability of an effective ingredient, but also excellent absorbability on oral administration, Patent Document 1 and 2 do not describe any crystals of Compound 1, nor the stability and oral absorbability of the crystals.